powerpc/32: prepare shadow area for KASAN

This patch prepares a shadow area for KASAN.

The shadow area will be at the top of the kernel virtual
memory space above the fixmap area and will occupy one
eighth of the total kernel virtual memory space.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/Kconfig.debug

@@ -366,3 +366,8 @@ config PPC_FAST_ENDIAN_SWITCH
         depends on DEBUG_KERNEL && PPC_BOOK3S_64
         help
 	  If you're unsure what this is, say N.
+
+config KASAN_SHADOW_OFFSET
+	hex
+	depends on KASAN
+	default 0xe0000000

arch/powerpc/include/asm/fixmap.h

@@ -22,7 +22,12 @@
 #include <asm/kmap_types.h>
 #endif
 
+#ifdef CONFIG_KASAN
+#include <asm/kasan.h>
+#define FIXADDR_TOP	(KASAN_SHADOW_START - PAGE_SIZE)
+#else
 #define FIXADDR_TOP	((unsigned long)(-PAGE_SIZE))
+#endif
 
 /*
  * Here we define all the compile-time 'special' virtual

arch/powerpc/include/asm/kasan.h

@@ -12,4 +12,20 @@
 #define EXPORT_SYMBOL_KASAN(fn)
 #endif
 
+#ifndef __ASSEMBLY__
+
+#include <asm/page.h>
+
+#define KASAN_SHADOW_SCALE_SHIFT	3
+
+#define KASAN_SHADOW_START	(KASAN_SHADOW_OFFSET + \
+				 (PAGE_OFFSET >> KASAN_SHADOW_SCALE_SHIFT))
+
+#define KASAN_SHADOW_OFFSET	ASM_CONST(CONFIG_KASAN_SHADOW_OFFSET)
+
+#define KASAN_SHADOW_END	0UL
+
+#define KASAN_SHADOW_SIZE	(KASAN_SHADOW_END - KASAN_SHADOW_START)
+
+#endif /* __ASSEMBLY */
 #endif

arch/powerpc/mm/mem.c

@@ -310,6 +310,10 @@ void __init mem_init(void)
 	mem_init_print_info(NULL);
 #ifdef CONFIG_PPC32
 	pr_info("Kernel virtual memory layout:\n");
+#ifdef CONFIG_KASAN
+	pr_info("  * 0x%08lx..0x%08lx  : kasan shadow mem\n",
+		KASAN_SHADOW_START, KASAN_SHADOW_END);
+#endif
 	pr_info("  * 0x%08lx..0x%08lx  : fixmap\n", FIXADDR_START, FIXADDR_TOP);
 #ifdef CONFIG_HIGHMEM
 	pr_info("  * 0x%08lx..0x%08lx  : highmem PTEs\n",

arch/powerpc/mm/ptdump/ptdump.c

@@ -100,6 +100,10 @@ static struct addr_marker address_markers[] = {
 #endif
 	{ 0,	"Fixmap start" },
 	{ 0,	"Fixmap end" },
+#endif
+#ifdef CONFIG_KASAN
+	{ 0,	"kasan shadow mem start" },
+	{ 0,	"kasan shadow mem end" },
 #endif
 	{ -1,	NULL },
 };
@@ -323,6 +327,10 @@ static void populate_markers(void)
 #endif
 	address_markers[i++].start_address = FIXADDR_START;
 	address_markers[i++].start_address = FIXADDR_TOP;
+#ifdef CONFIG_KASAN
+	address_markers[i++].start_address = KASAN_SHADOW_START;
+	address_markers[i++].start_address = KASAN_SHADOW_END;
+#endif
 #endif /* CONFIG_PPC64 */
 }